Chitosan-based polyelectrolyte complexes (CH PECs) have attracted significant attention as multifunctional carriers for advanced drug delivery. Formed through non-covalent interactions between chitosan (CH) and anionic polyelectrolytes, these systems offer advantages such as biocompatibility, biodegradability, mucoadhesion, and pH-responsive drug release. This chapter provides an in-depth overview of CH PECs, focusing on their formation mechanisms, physicochemical properties, preparation techniques, and characterization methods. The influence of critical parameters such as the degree of deacetylation, molecular weight, polymer ratios, and pH on complex stability, drug encapsulation efficiency, and release kinetics is thoroughly discussed. Applications across various administration routes, including oral, buccal, ocular, nasal, pulmonary, dermal, transdermal, vaginal, and parenteral delivery, are reviewed, highlighting the ability of CH PECs to enhance drug solubility, prolong therapeutic action, and improve bioavailability. The chapter also addresses translational challenges related to large-scale manufacturing, regulatory requirements, and in vivo performance. Overall, CH PECs represent a promising platform for the development of next-generation drug delivery systems capable of overcoming limitations of conventional formulations and facilitating clinical translation.